Evidence for this remains strong and as a result FA and multivitamin supplements are routinely recommended to pregnant women as well as fortification guidelines for food.

However, critics point to a body of evidence that identifies folate/folic acid’s role in masking vitamin B12 deficiency, which can lead to a form of neurological problems.

This observation has in turn been refuted as based on outdated and widely discredited data from the 1940s.

Study details ​

The research team, based at the University of Haifa in Israel, only used Israeli children born between January 1, 2003, and December 31, 2007.

They were followed up from birth to January 26, 2015, for the risk of ASD. The cases were all children diagnosed with ASD and the controls were a random sample of 33% of all live-born children.

Maternal vitamin supplements were classified for folic acid (vitamin B9), multivitamin supplements (vitamins A, B, C, and D), and any combination thereof exposed in the intervals before and during pregnancy.

Maternal exposure to folic acid and/or multivitamin supplements before pregnancy was statistically significantly associated with a lower likelihood of ASD in the offspring compared with no exposure before and during pregnancy.

“Our results are consistent with those from a Norwegian birth cohort ​study​​​ showing that maternal FA use from 4 weeks before and 8 weeks into pregnancy is associated with a reduced risk of ASD in offspring,”​ the study said.

“Maternal exposure to FA and multivitamin supplements two years before pregnancy was associated with a reduced risk of ASD in offspring. The risk of ASD associated with maternal vitamin exposure was similar before and during pregnancy.”​

CRN advice for folic acid​

In a similar study, published in JAMA Neurology​, researchers concluded that the risk of autistic traits in children exposed to antiepileptic drugs (AEDs) in utero may be lessened by folic acid supplementation at the periconceptional stage.

The Norwegian team’s advice advocating the continued use of folic acid supplements in fertile women received support from the Council of Responsible Nutrition’s (CRN) vice president of scientific & regulatory affairs, Dr Andrea Wong.

“Supplementing with folic acid by women who are pregnant, or capable of becoming pregnant, has proven essential to reduce neural tube birth defects in babies.”​

“Although this study points to the reduction of autistic traits associated with folic acid supplementation in a specific population—women taking antiepileptic drugs—it underscores the importance for all women capable of becoming pregnant to supplement with folic acid, too,”​ she added.